Plastic piping, especially in smaller diameter sizes, is rapidly becoming the material of preference in many piping applications. It is lightweight, less expensive and more corrosion resistant than most conventional metal systems.
The idea of joining dissimilar plastic pipes together is not new. Mechanical couplings have been used since plastic pipe was first developed. Most mechanical coupling devices arc typically metal sleeves, bolted around the outside of the pipe, where they are exposed to the environmental conditions that can corrode them over time.
Different piping materials obviously have different properties, and different plastics also have distinct properties. Polyolefins, like polyethylene (PE) and polypropylene (PP), can be coiled in long lengths, minimizing the number of joints. The normal procedure for jointing olefin piping is heat fusion, as this type of plastic cannot be glued or solvent-welded. In heat-fusion joining, both elements being joined are heated to melting temperature and fused as they cool in contact with one another. The heat fusion procedure can be affected by many variables, such as ambient temperature, the presence of moisture, operator error in handling the temperature settings and joining pressures.
Other types of plastic pipe are commonly glued or welded together using solvents. Common glueable or solvent-welded pipe like polyvinyl chloride (PVC), is rigid and is shipped in straight lengths, typically twenty feet long. Glued or solvent-welded joints are labor intensive and still frequently suffer from assembler error because of faulty welds or improper installation technique.